Monday 7 March 2016

Mapping Mountains – Hill Reclassifications – 30m – 99m Twmpau


Moel y Gadair (SH 521 391) 30-99m Twmpau reclassified to 30-99m Sub-Twmpau


This hill has subsequently been reinstated to 30-99m Twmpau status due to LIDAR analysis indicating this hill is a natural P30, with the raised road passing over the bwlch considered a relatively recent man-made construct; therefore it is excluded from the height of the bwlch.


There has been a reclassification to the listing of 30-99m Twmpau (thirty welsh metre prominences and upward) due to a survey with the Trimble GeoXH 6000 and subsequent LIDAR analysis.  The hill is listed in the 30–99m height band of Twmpau hills and is situated to the south-west of the small community of Pentrefelin, which is situated between Porthmadog to the east and Cricieth to the south-west.

The hill has been reclassified from a 30-99m Twmpau to a 30-99m Sub-Twmpau, and re-joins these ranks after being originally listed in the Hills to be surveyed Sub-List that appeared on Geoff Crowder’s v-g.me website.  On reassessment the hill was promoted to full P30 status due to bwlch contour interpolation, with a drop value of c 30m based on a summit spot height of 67m and an estimated bwlch height of c 37m.

The hill is named Moel y Gadair and its summit was surveyed with the Trimble GeoXH 6000 on the 15th June 2015 giving a height of 66.7m.  During the 15th June 2015 survey the contours at the bwlch were misinterpreted resulting in the second bwlch survey which was conducted on the 23rd February 2016 and the subsequent LIDAR analysis resulting in a bwlch height of 36.8m.

Therefore, the reclassification of this hill to 30-99m Sub-Twmpau status is due to a 66.7m summit height and a 36.8m bwlch height, with these values giving this hill 29.9m of drop which is insufficient for 30-99m Twmpau status.


The full details for the hill are:

Group:  Moel Hebog

Summit Height:  66.7m (converted to OSGM15)

Name:  Moel y Gadair

OS 1:50,000 map:  124

Summit Grid Reference:  SH 52165 39135

Drop:  29.9m (Trimble summit and LIDAR bwlch)


Moel y Gadair (SH 521 391) now reclassified from a 30-99m Twmpau to a 30-99m Sub-Twmpau

For details on the summit survey and the bwlch survey that resulted in this hill being reclassified to a 30-99m Sub-Twmpau status.

My thanks to Aled Williams for his initial LIDAR analysis

Myrddyn Phillips (February 2016)




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